Fan assisted heat sink device

ABSTRACT

A fan assisted heat sink cooling device is disclosed in which the heat sink assembly also forms the housing surrounding the fan. The housing is constructed of a plurality of cooling vanes which have elongated openings therebetween allowing air to pass between and cool the vanes. The vanes are angled in an approximately opposite manner to the orientation of the fan blades in order to minimize the noise generated by the cooling device when in operation. The cooling device operates in an extremely efficient manner by causing air to pass over the cooling vanes twice.

This application is a continuation of application Ser. No. 08/593,185filed Feb. 1, 1996, now U.S. Pat. No. 5,785,116, which is herebyincorporated by reference for all that is disclosed therein.

FIELD OF THE INVENTION

The present invention relates generally to cooling devices and, moreparticularly, to a cooling device for removing heat from an integratedcircuit device.

BACKGROUND OF THE INVENTION

Integrated circuit devices are increasingly being used in modernelectronic applications. One prevalent example is the computer. Thecentral processing unit or units of most computers, including personalcomputers, is constructed from an integrated circuit device.

During normal operation, integrated circuit devices generate significantamounts of heat. If this heat is not continuously removed, theintegrated circuit device may overheat, resulting in damage to thedevice and/or a reduction in operating performance. In order to avoidsuch overheating, integrated circuit cooling devices are often used inconjunction with integrated circuit devices.

One such cooling device is a fan assisted heat sink cooling device. Insuch a device, a heat sink is formed of a material, such as aluminum,which readily conducts heat. The heat sink is usually placed on top ofand in contact with the integrated circuit device. Due to this contact,heat generated by the integrated circuit is conducted into the heat sinkand away from the integrated circuit.

The heat sink may include a plurality of cooling fins in order toincrease the surface area of the heat sink and, thus, maximize thetransfer of heat from the heat sink device into the surrounding air. Inthis manner, the heat sink draws heat away from the integrated circuitand transfers the heat into the surrounding air.

In order to enhance the cooling capacity of such a heat sink device, anelectrically powered fan is often mounted on top of the heat sink. Inoperation, the fan causes air to move over and around the fins of theheat sink device, thus cooling the fins by enhancing the transfer ofheat from the fins into the ambient air.

Over the years, as the power of integrated circuit devices hasincreased, so has the amount of heat generated by these devices. Inorder to adequately cool these higher powered integrated circuitdevices, integrated circuit cooling devices with greater coolingcapacities are required.

Conventionally, the cooling capacity of fan assisted heat sink coolingdevices has been increased by making the devices larger. Specifically,cooling devices are often made larger by the incorporation of largerheat sinks and larger fans. This increase in size, however, has beenfound to present a problem. Increasing the size of the cooling device ina vertical direction (i.e. in a direction transverse to the orientationof the integrated circuit device) is often a problem because of thelimited envelope available in many applications, such as in the computercase of a desktop personal computer. This is an even greater problembecause, in most situations, a fairly substantial clearance area isrequired between the fan opening and the computer case to allow adequateairflow into or out of the fan.

Increasing the size of the cooling device in a horizontal direction(i.e. in a direction parallel to the orientation of the circuit board)is also often a problem because this limits the number of integratedcircuit devices (and other electronic devices) which may be incorporatedinto the computer case.

Another problem with fan assisted heat sink cooling devices is the noisegenerated by the fans, particularly in situations where larger fans areused to achieve increased cooling capacity. This is particularly aproblem in desktop computers where a user is commonly in close proximityto the machine. The problem is further aggravated in situations wheremultiple integrated circuit devices, and, thus, multiple coolingdevices, are mounted in the same computer case, as occurs in many highpower computers.

Thus, it would be generally desirable to provide an apparatus whichovercomes these problems associated with fan assisted heat sink devices.

SUMMARY OF THE INVENTION

The present invention is directed to a fan assisted heat sink coolingdevice primarily for cooling integrated circuits during operation.

The cooling device is provided with a heat sink assembly that also formsthe housing surrounding the fan. In this manner, the vertical size ofthe cooling device is minimized. The housing is constructed of aplurality of cooling vanes which have elongated openings therebetweenallowing air to pass between and cool the vanes.

The cooling device is also designed to generate significantly less noisewhile operating. To accomplish this, the cooling vanes are angled in anapproximately opposite manner to the angle of the fan blades. It hasbeen found that this configuration significantly reduces the noisegenerated by the cooling device.

The configuration of the cooling device causes it to operated in anextremely efficient manner. Because the fan housing is constructed froma series of vanes, air is caused to enter the housing through thehousing wall as well as from the open top of the housing. Accordingly,the cooling device is able to operate with a much smaller overheadclearance. Also, air being exhausted from the cooling device is causedto pass over the housing vanes a second time, thus further enhancingheat dissipation.

Air is exhausted from the housing through a series of curved slots whichare aligned with the orientation of the fan blades. This arrangementresults in a highly efficient air flow path for increased cooling deviceefficiency.

The heat sink assembly may be integrally formed to prevent heatconductance losses ordinarily associated with joints. A large mass ofheat conductive material is provided in the heat sink assemblyimmediately adjacent the integrated circuit device to enhance heat flowfrom the integrated circuit device into the heat sink.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front perspective view of a cooling device.

FIG. 2 is a front elevation view of a fan assembly used in the coolingdevice of FIG. 1.

FIG. 3 is a schematic front perspective view of the volume swept by thefan blades of the fan assembly of FIG. 2.

FIG. 4 is a bottom perspective view of a heat sink assembly used in thecooling device of FIG. 1.

FIG. 5 is a side elevation view of the heat sink assembly of FIG. 4.

FIG. 6 is a top plan view of the heat sink assembly of FIG. 4.

FIG. 7 is a cross section view of the heat sink assembly of FIG. 4 takenalong the line 7--7 of FIG. 6.

FIG. 8 is front elevation view of the cooling device of FIG. 1 mountedon an integrated circuit board.

FIG. 9 is a cut-away detail view of a portion of the fan assembly ofFIG. 2.

FIG. 10 is a partial plan view of the fan assembly of FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1-9, in general, illustrate a cooling device 10 for dissipatingheat from a heat source 110. The cooling device 10 may include asubstantially planar surface 54 adapted to contact the heat source 110and a peripheral wall portion 82 which defines a chamber 84 therewithin.The chamber 84 may have a first open end 85 and a second closed enddefined by a chamber wall portion 86. The cooling device may alsoinclude a heat conductive base portion 52 located between the planarsurface 54 and the chamber wall portion 86. A plurality of openings 73extend through the peripheral wall portion 82 and also into the baseportion 52.

FIGS. 1-9 also illustrate, in general, a cooling device 10 fordissipating heat from a heat source 110, the cooling device 10 includinga fan chamber 84 defined by a plurality of cooling vanes 71, each of thecooling vanes 71 having a central longitudinal axis "VV", FIG. 5, and aplurality of fan blades 21 rotatably mounted about a fan rotation axis"AA" within the fan chamber 84, each of the fan blades 21 having a fanblade orientation axis "FF". Each of the cooling vane centrallongitudinal axes "VV" forms an angle "y" of between about 75 and 105degrees with respect to the fan blade orientation axis "FF".

FIGS. 1-9 also illustrate, in general, a method of removing heat from aheat source 110 including the steps of providing a heat sink assembly 50having an interface surface 54, a peripheral wall portion 82 defining achamber 84 therewithin and a heat conductive base portion 52 locatedbetween the interface surface 54 and the chamber 84; contacting the heatsource 110 with the interface surface 54; causing air 148, 150 to moveinto the chamber 84 through the peripheral wall portion 82; and causingair 144, 146 to move out of the chamber 84 through the base portion 52.

Having thus described the cooling device in general, the device will nowbe described in further detail.

FIG. 1 illustrates a cooling device 10 which includes a fan assembly 20mounted within a heat sink assembly 50. As shown in FIG. 2, fan assembly20 includes a plurality of fan blades 21, such as the individual blades22, 24 and 26. The fan blades may be mounted on a hub assembly 28 whichmay, in turn, be rotatably mounted on the shaft 32 of a base member 30.Hub assembly 28 may be rotatably driven with respect to shaft 32 by amotor, not shown, located within the hub assembly 28. Fan assembly 20has a central longitudinal axis "AA" which is also the axis about whichthe hub assembly 28 rotates when the fan assembly is activated.Electrical wires 34, 36 may enter the fan assembly 20 through the basemember 30, as shown, in order to supply electric power to the fanassembly motor. A third wire, not shown, may optionally be connected tothe fan assembly 20 in order to monitor fan rotation. In this manner,the integrated circuit device being cooled by the cooling device 10 maybe shut down if the fan 20 fails to rotate at a specified speed, thuspreventing overheating of the integrated circuit device.

Hub assembly 28 may have a diameter "a" of about 37 mm and may have aheight "b" of about 15 mm which may be substantially the same as theheight of the fan blades. The diameter "c" to the outside of the fanblades may be about 55 mm. The overall height "d" of the fan assembly 20may be about 25 mm.

As schematically illustrated in FIG. 3, the fan blades, when rotatingand viewed from above, define an annular area 38. Annular area 38 has aninside diameter equal to the hub assembly diameter "a" and an outsidediameter equal to the fan blade diameter "c". Using the exampledimensions listed above, this yields an annular area 38 having an innerdiameter of about 37 mm, an outer diameter of about 55 mm and an area ofapproximately 13 square cm. The fan blades, when rotating, also definean annular volume 40. Annular volume 40 has a cross-sectional areaidentical to the area 38 described above and a height equal to the fanblade height "b". Using the example dimensions listed above, this yieldsan annular volume having a cross-sectional area of approximately 13square cm, a height of about 15 mm and a volume of approximately 19.5cubic cm.

The annular volume 40 described above, which also may be referred toherein as the "blade swept space" 40, is defined by the rotation of thefan blades 21 as illustrated in FIG. 3.

The fan assembly motor may be a 12 volt DC brushless motor. The fanassembly 20 may be of the type commercially available from MatsushitaElectric Company of Japan, sold as Model FBA06A12H and under the tradename "PANAFLO" (with its housing removed).

Heat sink assembly 50 is shown in further detail in FIGS. 4-7. Heat sinkassembly 50 may be of generally cylindrical shape, and may have anoutside diameter "k" of about 73 mm and a height "l" of about 36 mm,FIG. 7. Heat sink assembly 50 may be formed from any heat conductivematerial, such as aluminum or copper. Heat sink assembly 50 includes aheat conductive base portion 52 having a lower surface 54, FIG. 4. Heatsink assembly base portion 52 may have a diameter which is equal to thediameter "k" of the heat sink assembly and a height "o" of about 16 mm,FIG. 7. Base portion lower surface 54 may contain a plurality of bores56, 58, 60, 62, FIG. 4. These bores may be provided to allow clearancefor projections which sometimes exist on electronic components such asthe component 110, FIG. 8. A plurality of threaded openings 64, 66, 68,70 may also be provided in lower surface 54.

Extending upwardly from the base portion 52 is an annular wall portion82, FIGS. 6 and 7. As can be seen from FIG. 7, annular wall portion 82may have a thickness "e" of about 7.65 mm and a height "i" of about 20mm. Annular wall portion 82 has an outer surface 81, which forms part ofthe outer surface of the heat sink device 50, and an inner surface 83.

A generally cylindrically shaped fan chamber 84 is located within theannular wall portion 82, with the outer wall of the fan chamber 84 beingdefined by the annular wall portion inner surface 83. The upper end offan chamber 84, as viewed in FIG. 7, may comprise an opening 85. Thelower end of fan chamber 84 may be defined by a lower surface 86. Fanchamber 84 may have a diameter "f" of about 58 mm and a height "i" ofabout 20 mm.

A counterbore 88 may be provided in the center of fan chamber lowersurface 86, extending downwardly into the base portion 52 of the heatsink assembly 50. Counterbore 88 includes a lower surface 90 and anupwardly extending circumferential sidewall 92, FIG. 7. Counterbore 88may have a diameter "g" of about 38 mm and a height "h" of about 6 mm.As best shown in FIGS. 6 and 7, counterbore sidewall 92 may include anotch 96.

Referring to FIGS. 4-7, the outer periphery of heat sink assembly 50includes a plurality of angled slots 73, such as the individual slots 74and 78. As best seen in FIG. 6, the slots, e.g., slots 74, 78, extendcompletely through the annular wall portion 82. A plurality of coolingvanes 71, such as the individual vanes 72, 76 and 80, are defined by theslots 73, such that there is a vane located between every two slotsaround the periphery of annular wall portion 82. As can be seen, theslots 73 open into the fan chamber 84 and allow air to move between theoutside of the heat sink assembly 50 and the fan chamber 84 through theannular wall portion 82 as will be explained in more detail. As can beseen from FIG. 7, the slots 73 and vanes 71 also extend below theannular wall portion 82 and into the heat sink assembly base portion 52.

The configuration of the cooling vanes 71 making up the heat sinkannular wall portion 82 will now be described in detail. The size ofeach of the cooling vanes 71 depends upon the number of vanes formingthe annular wall portion 82 and upon the width "N" of the slots 73, FIG.5. It is pointed out that, although the drawing figures show a specificnumber of vanes and slots for illustration purposes, any number of vanesand slots may be used in the cooling device 10. A preferredconfiguration, which has been found to provide for efficient air flowand heat transfer, is described below. Such a configuration may beconstructed having 45 cooling vanes, 45 slots, and be of a size aspreviously described.

Referring to FIG. 5, it can be seen that each of the cooling vanes 71,at the outer surface 81 of annular wall portion 82 may have a thickness"m" of about 2.2 mm, measured in a direction normal to the vaneinclination. Each vane may taper to a thickness of about 1.35 mm at theinner edge 83 of annular wall portion 82, measured in a direction normalto the vane inclination.

Because the vanes taper toward the inner edge 83 of annular wall portion82, the slots 73 may be formed having a relatively constant width acrossthe annular wall portion 82. This constant width is important inproviding for efficient air flow through the slots 73 between theexterior of cooling device 10 and the fan chamber 84. Each of the slots73, may have a thickness "n" of about 2 mm, FIG. 5.

As can be seen from FIGS. 4 and 7, the slots 73 extend below annularwall portion 82 and into the heat conductive base portion 52. The slotsin the base portion 52 define upwardly facing openings 97 in the fanchamber lower surface 86. The bottom portions of the slots 73 terminatein curved surface portions, such as the curved surface portion 75 shownin FIG. 5. These curved portions cause the airflow through the coolingdevice 10 to change from the vertical airflow path 138, 139 to thehorizontal exhaust flow path 144, 146 as will be described in furtherdetail with reference to FIG. 8. The provision of curved surfaces, suchas the curved surface 75, allows for a smooth, energy efficienttransition from the vertical airflow path 138, 139 to the horizontalairflow path 144, 146 and, thus, contributes to the overall efficiencyof the cooling device 10.

When the fan assembly 20 is inserted into the heat sink assembly 50, asshown in FIG. 1, the fan assembly base member 30, FIG. 2, fits withinthe heat sink counterbore 88, FIG. 7. To securely fasten the fanassembly 20 to the heat sink assembly 50, a conventional adhesive may beapplied to either the lower surface 31 of the fan assembly base member30, FIG. 2, or to the lower wall 90 of the heat sink assemblycounterbore 88, or to both. In this manner, the fan assembly base member30 may be securely fastened within the heat sink counterbore 88 whileallowing the fan blades 21 to rotate freely within the fan chamber 84.Alternatively, the fan 20 may be secured within the heat sink assembly50 in any conventional manner.

The notch 96 is provided in the heat sink assembly counterbore 88 toallow clearance for the connection between the electrical wires 34 and36 and the fan base member 30 when the fan assembly 20 is inserted intothe heat sink assembly 50 as described above. The wires 34 and 36 may bepassed through slots in the base 86, such as the slots 98, 100, in orderto connect with a power source, not shown, located outside of the heatsink assembly 50.

When the fan assembly 20 is inserted into the heat sink assembly 50 asdescribed above, the fan swept space 40, FIG. 3 is entirely locatedwithin the heat sink assembly fan chamber 84, FIGS. 6,7. Accordingly,the heat sink assembly annular wall portion 82 completely surrounds thefan swept space 40, acting as both a heat transfer surface and as ahousing for the fan assembly 20. This configuration allows coolingdevice 10 to be very compact and efficient.

FIG. 8 illustrates the cooling device 10 mounted for use in a typicalcomponent cooling application. In the example shown, a component 110 ismounted on a PC board 120. Component 110 may be, for example, aprocessor such as a central processing unit for use in personal computerand work station applications. Component 110 may be mounted to the PCboard 120 via electrical connectors, such as the connectors 112, 114 ina conventional manner. In order to facilitate heat dissipation,component 110 may be provided with a lid 116 which is formed from a heatconductive material such as copper in a conventional manner.

Auxiliary components, such as those illustrated by the auxiliarycomponents 130, 140, are often located in close proximity to primarycomponents such as the component 110. Such auxiliary components may bemounted to the PC Board 120 as shown, for example by the connectors 132,134 in a conventional manner.

During operation, electronic components such as the components 110, 130,140 generate significant amounts of heat. This is particularly true withrecently developed more powerful components such as many of the computerprocessors currently in use. In order to keep such components operatingat peak efficiency and to avoid damage, overheating of the componentsmust be avoided. To prevent such overheating, it is necessary to removesufficient heat from the components during operation.

To accomplish heat removal from the primary component 110, coolingdevice 10 may be mounted directly on top of the component lid 116 sothat the lower surface 54 of the heat sink assembly base portion 52 isin contact with the upper surface of the component lid 116, forming ajoint 122 therebetween. In this manner, heat generated by the component110 may be conducted through the component lid 116 and into the baseportion 52 of the heat sink assembly 50. To facilitate heat transferacross the joint 122, a heat conductive substance, such as a heatconductive grease, may be applied between the lid 116 and the lowersurface 54 of the heat sink base portion 52 in a conventional manner.

Heat sink assembly 50 may be securely fastened to the PC board by theuse of threaded fasteners, such as the threaded fasteners 124 and 126shown in FIG. 8. The fasteners 124, 126 pass through holes, such as theholes 125, 127 in the PC board and threadingly engage with threadedopenings in the heat sink assembly 50, such as the threaded openings 64,66, 68 and 70, FIG. 4. It is noted that, although four threadedfasteners may be used to secure the heat sink assembly 50 to the PCboard, only two are shown in FIG. 8.

In this manner, the lower surface 54 of the heat sink assembly 50 may betightly secured against the upper surface of the component lid 116, thusfacilitating heat transfer between the two surfaces. Accordingly, heatis drawn away from the component 110 and into the relatively large baseportion 52 of the heat sink assembly 50. The heat is then furtherconducted upwardly into the cooling vanes 71, FIG. 4.

In order to facilitate drawing heat away from the component 110, theheat sink assembly 50 may be provided with a large base portion 52 asshown in FIG. 7. As described previously, base portion 52 may have adiameter substantially equal to the diameter "k" of the heat sinkassembly. Base portion 52 may also have a height "o" of approximately 16mm. This relatively large height "o" provides a large mass of heatconductive material between the heat sink assembly lower surface 54 andfan chamber 84 and thus acts as a large heatsink, thus facilitating theremoval of heat away from the component 110. Given the exemplarydimensions previously discussed, the height "o" of the base portion 52may be about 456 of the total height "l" of the heat sink assembly 50.For efficient heat transfer, the height "o" of the base portion 52should be at least 25% of the total height "l" of the heat sink assembly50.

For efficient cooling, the heat, after being transferred into the baseportion 52, must be further transferred into the cooling vanes 71 andthen into the surrounding air. The ability of a heat sink device, suchas heat sink assembly 50, to transfer heat into the air depends, amongother things, upon the amount of surface area of the heat sink deviceexposed to the surrounding air. The cooling vanes 71 facilitate suchheat transfer by effectively increasing the surface area of the heatsink device 50.

In operation, fan 20 may rotate in a counterclockwise direction, asviewed, for example, in FIG. 1. Referring to FIG. 8, thiscounter-clockwise fan rotation will cause air movement in the generaldirection of the arrows 138, 139. Specifically, intake air from theexterior of cooling device 10 will enter the heat sink assembly fanchamber 84 through the heat sink assembly opening 85, FIG. 7. This airmovement is indicated by the arrows 140, 142 in FIG. 8. After enteringthe fan chamber 84, the air moves downwardly, in a direction alignedwith the arrows 138, 139 through the fan swept space 40, FIG. 3, towardthe fan chamber lower surface 86, FIG. 7. Continuing its downwardmovement, the air enters the lower portion of the slots 73 throughupwardly facing openings 97, FIG. 7, in the fan chamber lower surface86. The air then travels down the lower portion of the slots 73 andexhausts from the cooling device as indicated by the arrows 144 and 146,FIG. 8. After exiting the cooling device 10, the horizontal airflow path144, 146 moves over and thus serves to cool auxiliary components, suchas the components 130, 140, located adjacent the component 110.

As the air moves through the lower portion of the slots 73, as describedabove, it also moves between the lower portions of the associated vanes71, located in the base portion 52, thereby cooling the vanes andremoving heat from the heat sink assembly 50.

The airflow 138, 139 moving through the fan chamber 84, results in aBernoulli effect as it passes the slots 73. This Bernoulli effectinduces an additional intake airflow, as indicated by the arrows 148 and150, FIG. 8. The airflow 148, 150 comprises air moving from the exteriorof the cooling device 10, through the upper portion of the slots 73 andinto the fan chamber 84. The airflow 148, 150 then joins the airflow140, 142 to form the airflow 138, 139 previously described.

By using the Bernoulli effect, the cooling device 10 is able to causemore air movement through the device than would be possible with aconventional configuration. Specifically, to provide for the Bernoullieffect described above, the annular wall 82 of the fan chamber 84 isprovided with the slots 73. The movement of the airflow 138, 139 pastthe slots 73 causes the Bernoulli effect and thus results in theincreased air movement previously described.

As the airflow 148, 150 moves through the upper portion of the slots 73,as described above, it also moves between the upper portions of theassociated vanes 71, thereby providing additional cooling of the vanes71, located in the annular wall portion 82, and removal of heat from theheat sink assembly 50.

As can be appreciated from the above description, each vane 71 of thecooling device 10 is cooled by two separate airflows. First, airflow148, 150 moves past an upper portion of the vanes 71 to cool the vanes.Thereafter, the airflow 144, 146 moves past a lower portion of the vanes73 to further cool the vanes. Accordingly, a portion of the air movingthrough the cooling device 10 is used twice for cooling; once on intakemaking up the airflow 148, 150 and a second time on exhaust partiallymaking up the airflow 144, 146.

As described above, the cooling device 10 is able to obtain intake airboth from the opening 85 and from the slots 73 surrounding the fanchamber 84. Because the cooling device 10 does not rely solely on thefan chamber opening 85 for intake air, the clearance provided above thecooling device 10 is less critical than with conventional designs. Ithas been found, for example, that the cooling device will operateefficiently with a clearance of as little as 2 mm above the opening 85.This ability to operate in low clearance applications is an extremelyadvantageous feature which allows the cooling device 10 to be used inspace sensitive applications and, particularly, in applications wherethe dimension normal to the orientation of the pc board 120 is limited.

Specifically, the cooling device 10, constructed according to theexemplary dimensions previously described, has a measured thermalresistance of about 0.35 degrees C. per watt with infinite clearanceabove the opening 85. In a conventional manner, this thermal resistancewas measured as the difference between the temperature of the lowersurface 54 and the ambient air divided by the watts of heat energy beingproduced by the heat source (e.g., component 110). When a solid plate isplaced approximately 2 mm above the opening 85, the measured thermalresistance of the cooling device 10 degrades only to about 0.38 degreesC. per watt. Accordingly, it can be appreciated that the thermalresistance of the cooling device 10 drops only about 9% when thevertical clearance above the opening 85 is reduced to about 2 mm.

Referring to FIG. 5, it can be seen that the heat sink assembly 50 has acentral longitudinal axis "BB", which is normal to the plane of the heatsink assembly lower surface 54 and which is also colinear with the fanassembly rotational axis "AA" when the fan assembly 20 is mounted withinthe heat sink assembly 50 as described above. With further reference toFIG. 5, it can be seen that each of the vanes 71 has a centrallongitudinal axis "VV". Each vane central longitudinal axis "VV" isinclined at an angle "w" with respect to the heat sink centrallongitudinal axis "BB". Because the slots 73 define the vanes 71, eachslot also has a central longitudinal axis which is inclined at the sameangle "w" with respect to the heat sink central longitudinal axis "BB".

It has been found that the vane inclination described above isinstrumental in reducing the noise produced by the cooling device 10when in operation. FIG. 9 illustrates the configuration of a singleblade 22 of the fan assembly 20. The blade 22 has an orientation axis"FF" which is inclined at an angle "x" with respect to the fan assemblycentral longitudinal axis "AA" in a conventional manner. When the fanassembly hub 28 rotates in a counter-clockwise direction, the blade 22moves generally in the direction of the arrow 152 in FIG. 9. Because ofthe inclination of the blade 22 described above, this movement resultsin air movement in a direction indicated by the arrow 154. The directionindicated by the arrow 154 is substantially perpendicular to the bladeorientation axis "FF".

Also shown, superimposed on FIG. 9 is the vane central longitudinal axis"VV" and the heat sink central longitudinal axis "BB". As previouslydescribed, the heat sink central longitudinal axis "BB" is colinear withthe fan assembly rotational axis "AA" when the fan assembly 20 ismounted within the heat sink assembly 50. As can be seen, the vanecentral longitudinal axis "VV" forms an angle "w" with respect to boththe fan assembly rotational axis "AA" and the heat sink centrallongitudinal axis "BB" as previously described. As can further be seen,the vane central longitudinal axis "VV" also forms an angle "y" withrespect to the blade orientation axis "FF". As can be appreciated froman examination of FIG. 9, adding the angles "w" and "x" always resultsin the angle "Y".

It has been found that, when the cooling device 10 is in operation, thenoise produced by the cooling device is significantly affected by theangle "y" between the vane central longitudinal axis "VV" and the bladeorientation axis "FF". Fan noise is a significant problem associatedwith cooling devices such as the cooling device 10 described herein.Such noise is a particular problem in situations where larger and/orhigher speed fans are used to achieve increased cooling capacity and indesktop computers where a user is commonly in close proximity to themachine. The noise problem is further aggravated in situations wheremultiple integrated circuit devices, and, thus, multiple coolingdevices, are mounted in the same computer case, as occurs in many highpower computers.

It has been found that the noise generated by cooling devices, such asthe cooling device 10, is at a maximum when the angle "y" is equal to 0degrees and that the noise is at a minimum when the angle "y" is equalto 90 degrees. Although the noise is minimized at an angle "y" of 90degrees, acceptable noise levels may be achieved using an angle "y" ofbetween about 75 degrees and about 105 degrees.

As can be appreciated, given a fan blade angle "x" of about 55 degrees(as is typical in many conventional fans), the cooling vane angle "w"will have a range of between about 20 degrees and 50 degrees when theangle "y" has a range of between about 75 degrees and 105 degrees asdescribed above. As can be further appreciated, the cooling vane angle"w" will be equal to about 35 degrees when the angle "y" is equal toabout 90 degrees and the fan blade angle "x" is equal to about 55degrees.

The vane angle configuration described above also results in anotherimprovement to the operation of the cooling device 10 as will now bedescribed in detail.

As previously described, the slots 73 in the heat sink assembly baseportion 52 define upwardly facing openings 97 in the fan chamber lowersurface 86, FIG. 6. These openings serve to provide an exhaust path forair exiting the fan chamber 84 during operation of the cooling device10. The bottom portions of the slots 73 terminate in curved surfacesportions, such as the curved portion 75 shown in FIG. 5. These curvedportions cause the airflow through the cooling device 10 to change fromthe vertical airflow path 138, 139 to the horizontal exhaust flow path144, 146 as described previously with reference to FIG. 8.

Referring again to FIG. 9, it can be appreciated that the slots 73 inthe base portion 52, as well as the upwardly facing openings 97, will beinclined at the same angle "y" with respect to the blade orientationaxis "FF". As previously described, the airflow direction 154, FIG. 9,is oriented at approximately 90 degrees with respect to the bladeorientation axis "FF". Accordingly, orienting the vane centrallongitudinal axis "VV" at approximately 90 degrees from the bladeorientation axis "FF", as described previously, will result in the airflow direction 154 being substantially aligned with the vane centrallongitudinal axis "VV" and, accordingly, with the slots 73, which areformed at the same inclination as the vanes 71, as previously explained.

This alignment of the air flow direction 154 and the exhaust openings 97and slots 73 results in a straight, smooth exhaust path for the airleaving the fan chamber 84. This configuration, thus, contributes to theefficiency of the cooling device 10 by reducing air flow shock lossesthat might otherwise be encountered in a conventional device.

Referring to FIG. 6, it can be seen that the heat sink assembly 50 has abisector line "HR--HR" which is perpendicular to the heat sink centrallongitudinal axis "BB", FIG. 5. With further reference to FIG. 6, it canbe seen that each of the slots 97 in the lower surface 86 has a slotcentral longitudinal axis "SS". Each slot central longitudinal axis "SS"is inclined at an angle "A" with respect to the heat sink bisector line"HR--HR".

It has been found that the slot inclination described above is alsoinstrumental in reducing the noise produced by the cooling device 10when in operation. FIG. 10 illustrates the configuration of a singleblade 22 of the fan assembly 20, as viewed from above. The fan assembly20 has a bisector line "FR--FR" which is perpendicular to the fanassembly central longitudinal axis "AA", FIG. 2, and to the heat sinkcentral longitudinal axis "BB", FIG. 5, when the fan assembly 20 isinstalled within the heat sink assembly 50 as previously described. Thebottom portion 185 of the blade 22 has an orientation axis "ZZ" which isinclined at an angle "B" with respect to the fan assembly bisector line"FR--FR" in a conventional manner.

Also shown, superimposed on FIG. 10 is the slot central longitudinalaxis "SS". As can be seen, slot central longitudinal axis "SS" forms anangle "C" with respect to the fan blade orientation axis "ZZ". As can beappreciated from an examination of FIG. 10, adding the angles "A" and"B" always results in the angle "C".

It has been found that, when the cooling device 10 is in operation, thenoise produced by the cooling device is significantly affected by theangle "C" between the slot central longitudinal axis "SS" and the fanblade orientation axis "ZZ". It has been found that the noise generatedby cooling devices, such as the cooling device 10, is at a maximum whenthe angle "C" is equal to 0 degrees and that the noise is at a minimumwhen the angle "C" is equal to 90 degrees. Although the noise isminimized at an angle "C" of 90 degrees, acceptable noise levels may beachieved using an angle "C" of between about 45 degrees and about 135degrees.

It is noted that, in the cooling device constructed according to theexemplary dimensions previously set forth, the angle "C" may be about 60degrees. As can be appreciated from an examination of FIGS. 6 and 10,increasing the angle "C" beyond about 60 degrees would also increase theangle "A" which would result in interference between adjacent openings97. It has been found, however, that an angle "C" of 60 degrees providessufficiently quiet operation.

It is also noted that other configurations of the cooling device may beutilized in which the angle "C" could be made to equal 90 degrees. Anexample would be a heat sink assembly 50 having a lesser number of slotsand wider cooling vanes. Such a configuration, for example, would allowadequate clearance so that an angle "C" of 90 degrees could be used formaximum noise reduction.

Although the heat sink assembly 50 may be constructed in anyconventional manner, a preferred method for its construction will now bedescribed.

First, an extruded solid round bar of, e.g., aluminum, may be provided,having substantially the same diameter as the outside diameter "k" ofthe heat sink assembly, FIG. 7.

The cylinder may then be machined, e.g., with a lathe, to the exactoutside diameter "k" of the heat sink assembly. A lathe may then againbe used, in a conventional manner, to form the fan chamber 84, having adiameter "f" and the counterbore 88 having a diameter "g".

A conventional end milling operation may be used to form the notch 96,as shown in FIG. 7. The slots 73 may then be formed using a circularslitting saw. After the slitting saw is oriented at the desired slot andvane inclination angle "w" and rotation angle "A", successive slots maybe cut, with the heat sink assembly being rotated an appropriatedistance relative to the slitting saw between each cut.

A cylinder having a height substantially equal to the heat sink assemblyheight "l", FIG. 7, is then cut from the bar. After cutting thecylinder, the heat sink assembly lower surface 54 may be milled flat andsmooth to facilitate reliable attachment to a heat source. Finally, thebores 56, 58, 60, 62 and threaded openings 64, 66, 68, 70 may bemachined into the lower surface 54.

To form a heat sink assembly having the exemplary dimensions set forthherein, the slitting saw used may have a diameter of approximately 4.0inches and a thickness of approximately 5/16 of an inch. As can beappreciated, the diameter of the slitting saw will dictate the curvatureof the slot bottom curved surface portions 75, FIG. 5.

Forming the heat sink assembly 50 as described above results in a heatsink unit of integral configuration. This is advantageous to theefficient removal of heat from a heat source since any joints in theheat sink assembly would tend to compromise heat transfer ability.

While an illustrative and presently preferred embodiment of theinvention has been described in detail herein, it is to be understoodthat the inventive concepts may be otherwise variously embodied andemployed and that the appended claims are intended to be construed toinclude such variations except insofar as limited by the prior art.

What is claimed is:
 1. A cooling device for dissipating heat from a heatsource comprising:a substantially planar surface adapted to contact saidheat source; a peripheral wall portion defining a chamber therewithin;said chamber having a first open end and a second closed end defined bya chamber wall portion; a heat conductive base portion located betweensaid planar surface and said chamber wall portion; at least one fanblade rotatably mounted about a fan rotation axis within said chamber; aplurality of slots extending through said peripheral wall portion, saidslots also extending into said base portion; at least one of saidplurality of slots defining a slot inclination axis in a planeperpendicular to said fan rotation axis; said at least one fan bladehaving an edge facing said chamber wall portion, wherein said edgedefines a fan blade orientation axis in a plane perpendicular to saidfan rotation axis; wherein said slot inclination axis forms an anglewith said fan blade orientation axis of between about 45 degrees andabout 135 degrees.
 2. The cooling device of claim 1 wherein said angleis about 60 degrees.
 3. The cooling device of claim 1 wherein said angleis about 90 degrees.
 4. A cooling device for dissipating heat from aheat source, said cooling device comprising:a substantially planarsurface adapted to contact said heat source; a cooling device centralaxis which is substantially perpendicular to said planar surface; achamber located within said cooling device; a chamber wall substantiallysurrounding said chamber, wherein said chamber wall includes at leastone cooling vane therein; wherein a second axis is substantiallyparallel to said cooling device central axis and intersects said atleast one cooling vane; and wherein said at least one cooling vane isinclined with respect to said second axis.
 5. The cooling device ofclaim 4 further including an air movement device located in saidchamber.
 6. The cooling device of claim 5 wherein said air movementdevice comprises a fan.
 7. The cooling device of claim 4 furtherincluding a heat conductive base portion located between said planarsurface and said chamber.
 8. The cooling device of claim 7 wherein saidat least one cooling vane comprises a plurality of cooling vanes whichsubstantially surround said base portion.
 9. The cooling device of claim4 wherein said at least one cooling vane is inclined with respect tosaid second axis at an angle of between about 20 degrees and about 50degrees.
 10. The cooling device of claim 4 wherein said at least onecooling vane is inclined with respect to said second axis at an angle ofabout 35 degrees.
 11. A cooling device for dissipating heat from a heatsource comprising:a) a surface adapted to contact said heat source; b) aperipheral wall portion defining a chamber therewithin; c) a heatconductive base portion located between said surface and said peripheralwall portion; d) a plurality of openings extending through saidperipheral wall portion; e) wherein said cooling device has a coolingdevice height measured in a direction substantially perpendicular tosaid surface; f) wherein said base portion has a base portion heightmeasured between said surface and said peripheral wall portion in adirection substantially perpendicular to said surface; and g) whereinsaid base portion height is about 45 percent of said cooling deviceheight.
 12. The cooling device of claim 11 wherein said plurality ofopenings also extend into said base portion.
 13. The cooling device ofclaim 12 wherein said plurality of openings extend substantially to saidsurface.
 14. The cooling device of claim 11 wherein said base portionheight is approximately 16 mm.
 15. The cooling device of claim 14wherein said cooling device height is approximately 36 mm.
 16. Thecooling device of claim 11 further including an air movement devicelocated in said chamber.
 17. The cooling device of claim 16 wherein saidair movement device comprises a fan.
 18. The cooling device of claim 11wherein said peripheral wall portion comprises a plurality of vaneshaving slots therebetween.
 19. The cooling device of claim 18 whereinsaid slots form said plurality of openings extending through saidperipheral wall portion.
 20. The cooling device of claim 11 wherein saidsurface, said base portion and said peripheral wall portion areintegrally formed.
 21. A cooling device for dissipating heat from a heatsource, said cooling device comprising:a) a substantially planarsurface; b) a cooling device central axis which is substantiallyperpendicular to said planar surface; c) a chamber located within saidcooling device, said chamber defined by a chamber wall; d) an airmovement device located within said chamber; e) at least one slotextending between said chamber and the exterior of said cooling device;f) said at least one slot having a slot surface lying at least partiallybetween said chamber and said substantially planar surface; g) whereinsaid slot surface includes a first point lying thereon and a secondpoint lying thereon and wherein said second point is further from saidcentral axis than said first point; and h) wherein said first point isfurther from said substantially planar surface than said second point.22. The cooling device of claim 21 wherein said at least one slotcomprises a plurality of slots.
 23. The cooling device of claim 21wherein said slot surface is arcuate.
 24. The cooling device of claim 21wherein said slots extend substantially to said substantially planarsurface.